This invention relates to telephone systems and more particularly to a dial plan mapper used for routing telephone calls to different telephone networks.
In order to provide adequate utility, a Voice over IP (VoIP)-based Internet Telephony system must provide connectivity to the hundreds of millions of telephones on today's Public Switched Telephone Network (PSTN). Circuit-switched telephony is based on the E.164 international addressing standard. Internet applications are based on the Internet Protocol (IP) address space and the Domain Name System (DNS). In order to provide telephony services over IP networks (VoIP), there must be a translation between E.164 addresses and Internet hosts.
There are many challenges to interconnecting these large systems, not the least of which is the different addressing schemes and signaling protocols used by the two systems. The E.164 addressing scheme used with PSTN comprises a string of 1–15 decimal digits with allocation by country and geographic area. VoIP on the other hand uses 32 bit IP addresses that are assigned to Internet hosts. The PSTN signaling protocol uses a Foreign Exchange Office (FXO), Foreign Exchange Station (FXS), or Ear and Mouth (E&M) for analog signaling and Q.931, Q.Sig or Common Channel Signaling System #7 (SS7) for digital signaling. VoIP uses H.323, Session Initiation Protocol & Session Description Protocol (SIP+SDP), Simple Gateway Control Protocol (SGCP), Media Gateway Control Protocol (MGCP) and many other types of signaling protocols.
Quality of Service (QoS) for PSTN and VoIP are also different. QoS for PSTN is based on one universal level with 300–3400 Hz voice channels, sampled at 8 kHz, and transmitted digitally as 64 kbps Pulse Code Modulation (PCM). QoS for VoIP varies from “best effort” to “guaranteed delay” and uses protocols such as Resource Reservation Protocol (RSVP) and packet scheduling algorithms such as Weighted Fair Queuing (WFQ).
Prior efforts to marry these two address spaces have attempted to embed one address space in the other. For example, host names are provided in the form 2048.264.508.1.pstn.net. Alternatively, every endpoint is required to have two addresses. None of these efforts have proven effective. Furthermore, these mapping schemes do not operate efficiently with locally administered short-cut dial plans, such as those used with a Private Branch Exchange (PBX).
Thus, a need remains for a single translation solution for efficiently mapping between different VoIP and circuit-switched telephone systems.